Conventionally there are information recording media such as driver's licenses, cash cards and credit cards, on which various kinds of personal information are recorded. To record personal information on an information recording medium, a magnetic strip, an IC chip, or a barcode is used. Among these, a barcode records personal information most easily and least expensively. Barcodes are widely used in various areas including the product distribution field; for example, a so-called PDF 417, stack-type encoded barcode is used for US driver's licenses. Note that two-dimensional barcodes in which the amount of information is increased by stacking one-dimensional barcodes have become widespread in recent years.
There are various methods to read personal information recorded in two-dimensional barcodes. For example, in one method, a subject (two-dimensional barcode) is imaged by a camera having a two-dimensional image sensor installed, and the obtained two-dimensional image data is analyzed to read personal information; in another method, a subject (a two-dimensional barcode) placed on a glass is optically read from the other side [of the glass] by a flat bed scanner. However, since the above-mentioned methods require expensive machines and spacious installation environments, they are not suitable for cash registers in department stores or personal uses, for example. Therefore, a swipe-type information reading device, in which the edge of a card is held by hand (held by fingers) and the card is swiped to read information recorded in the two-dimensional barcode, has been widely used at cash registers or for personal uses.
Among information recording media, there are cards on which not only a two-dimensional barcode is printed but also a portrait photo is placed. For example, on the plastic card 100 shown in FIG. 12, a two-dimensional barcode 101 is printed at the bottom and a portrait 102 is placed in the upper left-hand corner. Another example is the ID card disclosed in Patent reference 1 (see FIG. 5 of Patent reference 1), on which a barcode (portrait contents code) is printed at the bottom and an upper-body photograph is placed on the left side.
Cards having visual characteristics such as a portrait, fingerprint, or signature increase their security and reliability. For example, a portrait is placed on the card, and the characteristics of the portrait (the center positions and sizes of eyes, mouth and nose, etc.) are encoded and embedded in a two-dimensional barcode. In this way, even when the portrait is replaced with that of someone else's, the two-dimensional barcode and the replaced portrait are optically read and the characteristics of the [replaced] portrait and the characteristics of the portrait that are embedded in the two-dimensional barcode are simply compared to each other to prevent forgery.    [Patent Reference 1] Japanese Unexamined Patent Publication (Tokkai) No. 2001-52142 (FIG. 5)
However, even with a card that contains a two-dimensional barcode and a portrait to prevent forgery, when information on the card is read by a swipe-type information reading device that is used at cash registers or for personal uses, geometric distortion may be caused, resulting in deteriorated reading accuracy.
In other words, since the human operation of holding the edge of an information recording medium is involved for the swipe-type (manual type) information reading device, the information recording medium may not be swiped at a constant speed. If that's the case, jitter in the transporting direction is caused to image data recorded in the information reading device. As a result, the two-dimensional barcode image and the portrait image are distorted, deteriorating reading accuracy. Note that such a problem can occur even in an automatic information reading device if the transporting speed is changed due to breakdown of the device in the midst of transporting the card with a motor.
When a two-dimensional image sensor or flat bed scanner other than a swipe-type information reading device is used at cash registers or for personal uses, the human operation of swiping is not necessary; therefore, the two-dimensional barcode image or portrait image will not be distorted. However, as described above, these devices increase cost and require spacious installation environments, and thus they have many factors to prevent their widespread use in the market. For these reasons, there is a need for cards in which, even when the two-dimensional barcode image and/or portrait image are distorted, the distortion can be corrected.